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Production of xylooligosaccharides and cellulosic ethanol from steam-exploded barley straw

Álvarez, Cristina, Sáez, Felicia, González, Alberto, Ballesteros, Ignacio, Oliva, José Miguel, Negro, María José
Holzforschung 2018 v.73 no.1 pp. 35-44
agricultural wastes, barley straw, bioethanol, biorefining, cellulose, endo-1,4-beta-xylanase, enzymatic hydrolysis, ethanol, ethanol production, fermentation, glucose, hemicellulose, hydrolysis, liquids, raw materials, saccharification, steam, xylooligosaccharides
Agricultural residues, such as barley straw (BS), are attractive sources for the production of chemicals and fuels based on the biorefinery principle. In the present paper, BS was steam exploded at 180°C/30 min and then 90% of the cellulose and 60% of the hemicellulose were recovered in solid and liquid fractions respectively, which were used for ethanol and xylooligosaccharides (XOS) production. In the course of enzymatic hydrolysis (EH), different solid loading (SL) (10–20% w/v) and enzyme doses (15 and 30 FPU g⁻¹ glucan) were applied to optimize the yield of glucose concentrations, while 92 g l⁻¹ glucose was released at 20% SL and 30 FPU g⁻¹ glucan enzyme dosage. For ethanol production, two different process configurations were compared: separate hydrolysis and fermentation (SHF) or prehydrolysis with simultaneous saccharification and fermentation (PSSF). To transform the soluble hemicellulose into xylooligomers, two glycoside hydrolases (GH) families 10 and 11 endoxylanases were used. Reaction times, enzyme dose and several combinations of enzymes were optimized to maximize the conversion into XOS. Under the pretreatment conditions indicated above, 14 g of ethanol was obtained via the PSSF approach and 11.1 g of XOS (with DP2–DP6) was obtained per 100 g of raw material.